Battery

ABSTRACT

A battery includes a positive electrode including a positive electrode active material, a negative electrode, and an electrolytic solution including a nonaqueous solvent. The positive electrode active material includes a compound having a crystal structure belonging to a space group FM3-M and represented by Compositional Formula (1): Li x Me y O α F β , where, Me is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, B, Ce, Si, Zr, Nb, Pr, Ti, W, Ge, Mo, Sn, Bi, Cu, Mg, Ca, Ba, Sr, Y, Zn, Ga, Er, La, Sm, Yb, V, and Cr; and subscripts x, y, α, and β satisfy the following requirements: 1.7≤x≤2.2, 0.8≤y≤1.3, 1≤α≤2.5, and 0.5≤β≤2. The nonaqueous solvent includes a solvent having at least one fluoro group.

BACKGROUND 1. Technical Field

The present disclosure relates to a battery.

2. Description of the Related Art

Japanese Unexamined Patent Application Publication No. 7-037617discloses a positive electrode active material having a crystalstructure belonging to a space group R3-M and represented by the formulaLi_(w)M_(x)O_(y)X_(z) (where M represents Co, Ni, Mn, V, Fe, or Ti; Xrepresents at least one halogen element; and 0.2≤w≤2.5, 0.8≤x≤1.25,1≤y≤2, and 0<z≤1).

SUMMARY

One non-limiting and exemplary embodiment provides a battery having highreliability, which has been demanded in existing technology.

In one general aspect, the techniques disclosed here feature a batteryincluding a positive electrode including a positive electrode activematerial, a negative electrode, and an electrolytic solution including anonaqueous solvent. The positive electrode active material includes acompound having a crystal structure belonging to a space group FM3-M andrepresented by Compositional Formula (1): Li_(x)Me_(y)O_(α)F_(β), whereMe represents one or more elements selected from the group consisting ofMn, Co, Ni, Fe, Al, B, Ce, Si, Zr, Nb, Pr, Ti, W, Ge, Mo, Sn, Bi, Cu,Mg, Ca, Ba, Sr, Y, Zn, Ga, Er, La, Sm, Yb, V, and Cr; and the followingrequirements: 1.7≤x≤2.2, 0.8≤y≤1.3, 1≤α≤2.5, and 0.5≤β≤2 are satisfied.The nonaqueous solvent includes a solvent having at least one fluorogroup.

The present disclosure can achieve a battery having high reliability.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a schematic structure ofan example of the battery according to Embodiment 1;

FIG. 2 is a powder X-ray diffraction chart of the positive electrodeactive material of Example 1;

FIG. 3 is a cross-sectional view illustrating a schematic structure ofthe battery in Example 1;

FIG. 4 is a perspective view illustrating a schematic structure of thebattery in Example 1;

FIG. 5 is a diagram illustrating a schematic structure of the positiveelectrode plate in Example 1 and a method of producing the plate;

FIG. 6 is a diagram illustrating a schematic structure of the negativeelectrode plate in Example 1 and a method of producing the plate; and

FIG. 7 is a perspective view illustrating a schematic structure of thebattery in Example 1.

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described.

Embodiment 1

The batter according to Embodiment 1 includes a positive electrode, anegative electrode, and an electrolytic solution.

The positive electrode includes a positive electrode active material.

The electrolytic solution includes a nonaqueous solvent.

The positive electrode active material includes a compound having acrystal structure belonging to a space group FM3-M and represented byCompositional Formula (1):Li_(x)Me_(y)O_(α)F_(β)  (1)

In Formula (1), Me represents at least one selected from the groupconsisting of Mn, Co, Ni, Fe, Al, B, Ce, Si, Zr, Nb, Pr, Ti, W, Ge, Mo,Sn, Bi, Cu, Mg, Ca, Ba, Sr, Y, Zn, Ga, Er, La, Sm, Yb, V, and Cr (i.e.,one or more elements selected from the group).

In Formula (1), subscripts x, y, α, and β satisfy the followingrequirements:1.7≤x≤2.2,0.8≤y≤1.3,1≤α≤2.5, and0.5≤β≤2.

The nonaqueous solvent includes a solvent having at least one fluorogroup.

The structure described above prevents occurrence of a side reaction atthe interface between the electrolytic solution and the positiveelectrode active material represented by Compositional Formula (1).Accordingly, the reliability (e.g., discharge efficiency) of the batterycan be enhanced.

Some electrolytic solutions that have been used are cyclic carbonates(such as ethylene carbonate and propion carbonate) and linear carbonates(such as dimethyl carbonate and ethyl methyl carbonate). In thesenonaqueous solvents, a side reaction readily occurs at the interfacewith a positive electrode from which Li is extracted during a chargingoperation. Consequently, the battery has insufficient reliability.

In contrast, the battery including an electrolytic solution and apositive electrode active material according to Embodiment 1 can preventoccurrence of a side reaction. The factors thereof are probably asfollows.

That is, the nonaqueous solvent of the electrolytic solution accordingto Embodiment 1 has at least one fluoro group. The positive electrodeactive material represented by Compositional Formula (1) includes afluorine atom in its structure. Accordingly, at the interface with thesolvent having at least one fluoro group, the fluorine in the positiveelectrode active material and the fluorine in the solvent electricallyrepel each other. Consequently, the distance between the positiveelectrode active material and the solvent increases. Probably, becauseof this, the side reaction between the both is prevented.

The structure of Embodiment 1 can achieve a high-capacity battery.

For example, a lithium ion battery including the positive electrodeactive material containing the above-mentioned compound has a redoxpotential (Li/Li reference) of about 3.3 V and a capacity of about 220mAh/g or more.

In the above-mentioned compound when subscript x in CompositionalFormula (1) is smaller than 1.7, the usable amount of Li is small,leading to an insufficient capacity.

In the above-mentioned compound when subscript x in CompositionalFormula (1) is larger than 2.2 (in other words, when subscript y issmaller than 0.8), the amount of the transition metal usable for theredox reaction is reduced. As a result, a large amount of oxygen is usedin the redox reaction, leading to unstabilization of the crystalstructure and an insufficient capacity.

In the above-mentioned compound when subscript a in CompositionalFormula (1) is smaller than 1 (in other words, when subscript p islarger than 2), the influence of F having high electronegativity ishigh. As a result, the electron conductivity decreases, and the capacitybecomes insufficient.

In the above-mentioned compound when subscript a in CompositionalFormula (1) is larger than 2.5 (in other words, when subscript p issmaller than 0.5), the influence of F having high electronegativity islow. As a result, the cation-anion interaction is reduced. Consequently,the structure is unstabilized when Li is deintercalated, and thecapacity becomes insufficient.

In the positive electrode active material according to Embodiment 1, thecompound represented by Compositional Formula (1) has a crystalstructure belonging to a space group FM3-M (rock salt crystalstructure).

In Compositional Formula (1), the ratio of Li to Me is denoted by{Li_(x)/Me_(y)}.

In {Li_(x)/Me_(y)}, subscripts x and y satisfy: 1.7≤x≤2.2 and 0.8≤y≤1.3.

Accordingly, the ratio of Li to Me is theoretically1.31≤{Li_(x)/Me_(y)}≤2.75 and is larger than 1.

That is, the number of Li atoms for one Me atom is larger than those ofknown positive electrode active materials, such as LiMnO₂.

In the compound represented by Compositional Formula (1), it isconceivable that Li and Me are located at the same site.

Accordingly, the compound represented by Compositional Formula (1) canintercalate and deintercalate a larger amount of Li for one Me atomcompared to known positive electrode active materials, such as LiMnO₂.

Accordingly, the positive electrode active material for a batteryaccording to Embodiment 1 is suitable for achieving a high-capacitylithium ion battery.

In the layered structure defined by a space group R3-M, the layerstructure cannot be maintained when a large amount of Li is extractedand is collapsed.

In contrast, in a rock salt crystal structure defined by the space groupFM3-M as in the compound of the present disclosure, even if a largeamount of Li is extracted, the structure is not collapsed and can bestably maintained. Consequently, a high-capacity battery can beachieved.

In addition, the positive electrode active material according toEmbodiment 1 may mainly include the above-mentioned compound.

Such a structure can achieve a battery having a higher capacity.

Herein, the wording “mainly include” means that the positive electrodeactive material of Embodiment 1 includes, for example, 90 wt % or moreof the above-mentioned compound.

The positive electrode active material of Embodiment 1 mainly includesthe above-mentioned compound and may further include, for example,inevitable impurities or a starting material used in the synthesis ofthe above-mentioned compound, a byproduct, and a decomposition product.

The above-mentioned compound in the positive electrode active materialaccording to Embodiment 1 may be a compound of Compositional Formula (1)satisfying x+y=α+β=3.

Such a structure can achieve a battery having a higher capacity.

In Embodiment 1, Me may be one element selected from Mn, Co, Ni, Fe, Al,B, Ce, Si, Zr, Nb, Pr, Ti, W, Ge, Mo, Sn, Bi, Cu, Mg, Ca, Ba, Sr, Y, Zn,Ga, Er, La, Sm, Yb, V, and Cr.

Alternatively, Me may be a solid solution of two or more elementsselected from Mn, Co, Ni, Fe, Al, B, Ce, Si, Zr, Nb, Pr, Ti, W, Ge, Mo,Sn, Bi, Cu, Mg, Ca, Ba, Sr, Y, Zn, Ga, Er, La, Sm, Yb, V, and Cr.

In Embodiment 1, Me in Compositional Formula (1) may be one elementselected from Mn, Co, Ni, and Fe; a solid solution composed of Ni, Co,and Mn; or a solid solution composed of Ni, Co, and Al.

Such a structure can achieve a battery having a higher capacity.

In Embodiment 1, the above-mentioned compound of Compositional Formula(1) may satisfy 1.79≤x≤2.18.

Such a structure can achieve a battery having a higher capacity.

In Embodiment 1, the above-mentioned compound of Compositional Formula(1) may satisfy 1.89≤x≤2.

Such a structure can achieve a battery having a higher capacity.

In Embodiment 1, the above-mentioned compound of Compositional Formula(1) may satisfy 0.79≤β≤1.

Such a structure can achieve a battery having a higher capacity.

In Embodiment 1, Me may contain at least one selected from the groupconsisting of Mn, Co, and Ni.

Such a structure can achieve a battery having a higher capacity and highreliability.

In Embodiment 1, Me may be one element selected from Mn and Co or may bea solid solution composed of Ni, Co, and Mn.

Such a structure can achieve a battery having a higher capacity and highreliability.

In Embodiment 1, the compound of Compositional Formula (1) may satisfy1.79≤x≤2.18, 0.82≤y≤1.21, 1.5≤α≤2.5, and 0.5≤β≤1.5.

Such a structure can achieve a battery having a higher capacity and highreliability.

In Embodiment 1, the compound of Compositional Formula (1) may satisfyx=2, y=1, 1.5≤α≤2, and 1≤β≤1.5.

Such a structure can achieve a battery having a higher capacity and highreliability.

The battery in Embodiment 1 can be constituted as, for example, alithium ion secondary battery or a nonaqueous electrolyte secondarybattery.

That is, in the battery in Embodiment 1, for example, the negativeelectrode may include a negative electrode active material capable ofoccluding and releasing lithium (having characteristics of occluding andreleasing lithium) or lithium metal.

FIG. 1 is a cross-sectional view illustrating a schematic structure of abattery 1000 as an example of the battery according to Embodiment 1.

As shown in FIG. 1, the battery 1000 includes a positive electrode 21, anegative electrode 22, a separator 14, a case 11, a sealing plate 15,and a gasket 18.

The separator 14 is disposed between the positive electrode 21 and thenegative electrode 22.

The positive electrode 21, the negative electrode 22, and the separator14 are impregnated with an electrolytic solution.

The positive electrode 21, the negative electrode 22, and the separator14 form an electrode group.

The electrode group is accommodated in the case 11.

The case 11 is sealed with the gasket 18 and the sealing plate 15.

The positive electrode 21 includes a positive electrode currentcollector 12 and a positive electrode active material layer 13 disposedon the positive electrode current collector 12.

The positive electrode current collector 12 is made of, for example, ametal material (e.g., aluminum, stainless steel, or an aluminum alloy).

The case 11 may be used as the positive electrode current collectorwithout disposing the positive electrode current collector 12.

The positive electrode active material layer 13 includes the positiveelectrode active material in Embodiment 1.

The positive electrode active material layer 13 may optionally include,for example, a conducting agent, an ion conductivity auxiliary, and abinder.

The negative electrode 22 includes a negative electrode currentcollector 16 and a negative electrode active material layer 17 disposedon the negative electrode current collector 16.

The negative electrode current collector 16 may be made of, for example,a metal material (e.g., copper, nickel, aluminum, stainless steel, or analuminum alloy).

The sealing plate 15 may be used as the negative electrode currentcollector without disposing the negative electrode current collector 16.

The negative electrode active material layer 17 includes a negativeelectrode active material.

The negative electrode active material layer 17 may optionally include,for example, a conducting agent, an ion conductivity auxiliary, and abinder.

Examples of the negative electrode active material include metalmaterials, carbon materials, oxides, nitrides, tin compounds, andsilicon compounds.

The metal material may be an elementary metal or may be an alloy.Examples of the metal material include lithium metal and lithium alloys.

Examples of the carbon material include natural graphite, coke, carbonduring graphitization, carbon fibers, spherical carbon, artificialgraphite, and amorphous carbon.

From the viewpoint of capacity density, silicon (Si), tin (Sn), siliconcompounds, and tin compounds can be suitably used. The silicon compoundsand the tin compounds may be alloys or solid solutions.

Examples of the silicon compound include SiO_(x) (where 0.05≤x≤1.95). Acompound (alloy or solid solution) prepared by partially replacingsilicon in SiO_(x) with another element also can be used. Herein, theanother element is at least one element selected from the groupconsisting of boron, magnesium, nickel, titanium, molybdenum, cobalt,calcium, chromium, copper, iron, manganese, niobium, tantalum, vanadium,tungsten, zinc, carbon, nitrogen, and tin.

Examples of the tin compound include Ni₂Sn₄, Mg₂Sn, SnO_(x) (where,0≤x≤2), SnO₂, and SnSiO₃. These tin compounds may be used alone or incombination of two or more thereof.

The negative electrode active material may have any shape. A negativeelectrode active material having a known shape (such as particulate orfibrous shape) can be used.

The negative electrode active material layer 17 may be compensated(occluded) with lithium by any method. Specifically, for example, (a)lithium is deposited on the negative electrode active material layer 17by a gas phase method, such as vacuum deposition, or (b) lithium metalfoil and the negative electrode active material layer 17 are broughtinto contact with each other and are heated. In both methods, lithiumdiffuses into the negative electrode active material layer 17 by heat.In another method, lithium is electrochemically occluded in the negativeelectrode active material layer 17. Specifically, a battery is assembledwith a lithium-free negative electrode 22 and lithium metal foil(positive electrode). Subsequently, the battery is charged such thatlithium is occluded in the negative electrode 22.

Examples of the binder of the positive electrode 21 or the negativeelectrode 22 include poly(vinylidene fluoride), polytetrafluoroethylene,polyethylene, polypropylene, aramid resins, polyamides, polyimides,polyamideimides, polyacrylonitriles, poly(acrylic acid), poly(methylacrylate), poly(ethyl acrylate), poly(hexyl acrylate), poly(methacrylicacid), poly(methyl methacrylate), poly(ethyl methacrylate), poly(hexylmethacrylate), poly(vinyl acetate), poly(vinyl pyrrolidone), polyethers,polyethersulfones, hexafluoropolypropylene, styrene butadiene rubber,and carboxymethyl cellulose. Alternatively, the binder may be acopolymer of two or more materials selected from the group consisting oftetrafluoroethylene, hexafluoroethylene, hexafluoropropylene,perfluoroalkyl vinyl ethers, vinylidene fluoride,chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene,fluoromethyl vinyl ether, acrylic acid, and hexadiene.

Examples of the conducting agent of the positive electrode 21 or thenegative electrode 22 include graphite, carbon black, conductive fibers,graphite fluoride, metal powders, conductive whiskers, conductive metaloxides, and organic conductive materials. Examples of the graphiteinclude natural graphite and artificial graphite. Examples of the carbonblack include acetylene black, Ketchen black (registered trademark),channel black, furnace black, lamp black, and thermal black. Examples ofthe metal powder include aluminum powder. Examples of the conductivewhisker include zinc oxide whiskers and potassium titanate whiskers.Examples of the conductive metal oxide include titanium oxide. Examplesof the organic conductive material include phenylene derivatives.

As the separator 14, materials having a high ion permeability and asufficient mechanical strength can be used. Examples of such a materialinclude porous thin film, woven fabric, and nonwoven fabric.Specifically, the separator 14 is desirably made of a polyolefin, suchas polypropylene and polyethylene. A polyolefin separator 14 not onlyhas excellent durability but also can exhibit a shutdown function whenexcessively heated. The separator 14 has a thickness in a range of, forexample, 10 to 300 μm (or 10 to 40 μm). The separator 14 may be amonolayer film composed of one material or may be a composite film (ormultilayer film) composed of two or more materials. The separator 14 hasa porosity in a range of, for example, 30% to 70% (or 35% to 60%). Theterm “porosity” refers to the rate of the volume of holes to the totalvolume of the separator 14. The “porosity” is measured by, for example,a mercury press-in method.

The nonaqueous solvent included in the electrolytic solution accordingto Embodiment 1 includes a solvent having at least one fluoro group.

In the nonaqueous solvent, the volume rate of the solvent having atleast one fluoro group may be 20% or more.

Such a structure can achieve a battery having a higher capacity and highreliability.

The nonaqueous solvent may be composed of substantially only a solventhaving at least one fluoro group.

Such a structure can achieve a battery having a higher capacity and highreliability.

The wording “nonaqueous solvent is composed of substantially only asolvent having at least one fluoro group” means that “the nonaqueoussolvent includes only a solvent or solvents having at least one fluorogroup, except for unintentionally incorporated components, such asimpurities”.

The nonaqueous solvent may further include, for example, a functionaladditive.

In such a case, the wording “nonaqueous solvent is composed ofsubstantially only a solvent having at least one fluoro group” meansthat “nonaqueous solvent includes only a solvent or solvents having atleast one fluoro group, except for the components such as additives andunintentionally incorporated components, such as impurities”.

These additives may be mixed with the electrolytic solution in an amountof about 0.01 wt % to 10 wt %.

Examples of the additive for improving the reliability of a lithiumsecondary battery include organic compounds having unsaturated bonds,such as vinylene carbonate and vinylethylene carbonate; sulfonecompounds, such as 1,3-propane sulfone; dinitrile compounds, such asadiponitrile; and diisocyanate compounds, such as hexamethylenediisocyanate. Examples of the additive for improving the safety of thelithium secondary battery include organic compounds having phenylgroups, such as cyclohexylbenzene; phosphate compounds, such astrimethyl phosphate; and phosphazene compounds, such asphenoxypentafluorocyclotriphosphazene.

Examples of the solvent having at least one fluoro group include cycliccarbonates, such as fluoroethylene carbonate, difluoroethylenecarbonate, trifluoroethylene carbonate, fluoropropylene carbonate, andtrifluoropropylene carbonate.

Alternatively, the solvent having at least one fluoro group may be alinear carbonate, such as fluoromethyl methyl carbonate, difluoromethylmethyl carbonate, trifluoromethyl methyl carbonate, 1,2-difluoromethylcarbonate, 1-fluoroethyl methyl carbonate, 2-fluoroethyl methylcarbonate, 1,1-difluoroethyl methyl carbonate, 2,2-difluoroethyl methylcarbonate, 2,2,2-trifluoroethyl methyl carbonate, ethyl fluoromethylcarbonate, ethyl trifluoromethyl carbonate, 1-fluoroethyl ethylcarbonate, 2-fluoroethyl ethyl carbonate, 1,1-difluoroethyl ethylcarbonate, 2,2-difluoroethyl ethyl carbonate, and 2,2,2-trifluoroethylethyl carbonate.

Alternatively, the solvent having at least one fluoro group may be acyclic carboxylate, such as fluoro-γ-butyrolactone,difluoro-γ-butyrolactone, and fluoro-γ-valerolactone.

Alternatively, the solvent having at least one fluoro group may be alinear carboxylate, such as methyl fluoroacetate, methyldifluoroacetate, fluoromethyl acetate, difluoromethyl acetate,trifluoromethyl acetate, methyl 3-fluoropropionate, methyl3,3-difluoropropionate, methyl 3,3,3-trifluoropropionate, methyl2,2-difluoropropionate, fluoromethyl propionate, difluoromethylpropionate, trifluoromethyl propionate, fluoromethyl 3-fluoropropionate,2-fluoroethyl acetate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethylacetate, 1-fluoroethyl acetate, 1,1-difluoroethyl acetate, ethylfluoroacetate, ethyl difluoroacetate, ethyl 2,2,2-trifluoroacetate,2-fluoroethyl propionate, 2,2-difluoroethyl propionate,2,2,2-trifluoroethyl propionate, 1-fluoroethyl propionate,1,1-difluoroethyl propionate, ethyl 3-fluoropropionate, ethyl3,3-difluoropropionate, and ethyl 3,3,3-trifluoropropionate.

Alternatively, the solvent having at least one fluoro group may be anitrile, such as fluoroacetonitrile, difluoropropionitrile,trifluoropropionitrile, and trifluorobutyronitrile.

Alternatively, the solvent having at least one fluoro group may be asulfone, such as (trifluoromethyl) methylsulfone, (trifluoromethyl)ethylsylsulfone, (trifluoromethyl) butylsulfone, (2,2,2-trifluoroethyl)methylsulfone, and (2,2,2-trifluoroethyl) ethylsulfone.

These solvents may be included in the electrolytic solution alone.

Alternatively, a combination of two or more of these solvents may beincluded in the electrolytic solution.

The use of a fluorinated product of a carbonate or carboxylate as thesolvent having at least one fluoro group can achieve a battery having ahigher capacity and high reliability.

The nonaqueous solvent may include a cyclic solvent having at least onefluoro group and a linear solvent having at least one fluoro group.

Such a structure can achieve a battery having a higher capacity and highreliability.

The electrolytic solution according to Embodiment 1 may further includea lithium salt.

Examples of the lithium salt dissolved in the nonaqueous solvent includeLiClO₄, LiBF₄, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, and lithiumbis(oxalate)borate (LiBOB). The lithium salt may be at least oneselected from the group consisting of these salts.

Use of LiPF₆ as the lithium salt can improve the ionic conductivity orreliability.

The molar content of the lithium salt in the electrolytic solution isnot particularly limited and may be 0.5 mol/L or more and 2.0 mol/L orless.

The electrolytic solution according to Embodiment 1 may further includea solvent not having a fluoro group, an additive, or another component.

The solvent not having a fluoro group may be a generally knownnonaqueous solvent, such as ethylene carbonate and ethyl methylcarbonate.

The battery according to Embodiment 1 can be formed into various shapes,for example, a coin-like, cylindrical, rectangular, sheet-like,button-like, flat, or laminar battery.

Method of Producing Compound

An example of the method of producing the above-mentioned compoundincluded in the positive electrode active material of Embodiment 1 willnow be described.

The compound represented by Compositional Formula (1) can be producedby, for example, the following method.

A raw material including Li, a raw material including F, and a rawmaterial including Me are prepared. Examples of the Li-including rawmaterial include oxides, such as Li₂O and Li₂O₂; salts, such as LiF,Li₂CO₃, and LiOH; and lithium-transition metal composite oxides, such asLiMeO₂ and LiMe₂O₄. Examples of the F-including raw material include LiFand transition metal fluorides. Examples of the Me-including rawmaterial include oxides in various oxidation states, such as Me₂O₃;salts, such as MeCO₃ and MeNO₃; hydroxides, such as Me(OH)₂ and MeOOH;and lithium-transition metal composite oxides, such as LiMeO₂ andLiMe₂O₄. For example, when Me is Mn, examples of the Mn-including rawmaterial include manganese oxides in various oxidation states, such asMn₂O₃; salts, such as MnCO₃ and MnNO₃; hydroxides, such as Mn(OH)₂ andMnOOH; and lithium-transition metal composite oxides, such as LiMnO₂ andLiMn₂O₄.

These materials are weighed so as to give a molar ratio shown byCompositional Formula (1).

On this occasion, subscripts “x, y, α, and β” in Compositional Formula(1) can be varied within the range shown by Compositional Formula (1).

The weighed raw materials are, for example, mixed by a dry process or awet process for a mechanochemical reaction for 10 hours or more toprepare a compound represented by Compositional Formula (1). The mixingis performed with, for example, a mixer, such as a ball mill.

The compound substantially represented by Compositional Formula (1) canbe prepared by adjusting the raw materials and the mixing conditions forthe raw material mixture.

The use of a lithium-transition metal composite oxide as a precursor canfurther decrease the energy for mixing the elements. Consequently, thecompound represented by Compositional Formula (1) can have a higherpurity.

The composition of the resulting compound represented by CompositionalFormula (1) can be determined by, for example, inductively coupledplasma (ICP) emission spectral analysis and an inert gas fusion-infraredabsorption method.

The compound represented by Compositional Formula (1) can be identifiedby determining the space group of the crystal structure by powder X-rayanalysis.

As described above, the method of producing a positive electrode activematerial according to an aspect of Embodiment 1 involves a step (a) ofpreparing raw materials and a step (b) of a mechanochemical reaction ofthe raw materials to prepare a positive electrode active material.

The step (a) may involve a step of mixing a raw material including Liand F and a raw material including Me at a molar ratio of Li to Me of1.31 or more and 2.33 or less to prepare a raw material mixture.

On this occasion, the step (a) may involve a step of producing alithium-transition metal composite oxide serving as a raw material by aknown method.

The step (a) may involve a step of mixing raw materials at a molar ratioof Li to Me of 1.7 or more and 2.0 or less to prepare a raw materialmixture.

The step (b) may involve a step of mechanochemically reacting rawmaterials with a ball mill.

As described above, the compound represented by Compositional Formula(1) can be synthesized by a mechanochemical reaction of precursors(e.g., LiF, Li₂O, oxidized transition metal, and lithium-transitionmetal composite) with a planetary ball mill.

On this occasion, the compound can include a larger amount of Li byadjusting the mixing ratio of the precursors.

In contrast, in a solid phase method, the precursors are decomposed intomore stable compounds.

That is, the production process involving a reaction of the precursorsby a solid phase method cannot produce the compound having a crystalstructure belonging to a space group FM3-M and represented byCompositional Formula (1).

EXAMPLES Example 1

Synthesis of Positive Electrode Active Material

LiF and LiMnO₂ were weighed at a molar ratio LiF/LiMnO₂ of 1.0/1.0.

The resulting raw material and an appropriate amount of zirconia ballsof 3 mm diameter were put in a 45-cc zirconia container, and thecontainer was sealed in an argon glove box.

The sealed container was taken out from the argon glove box, followed bytreatment with a planetary ball mill at 600 rpm for 30 hours.

The resulting compound was subjected to powder X-ray diffractionanalysis.

FIG. 2 shows the results of the analysis.

The resulting compound was in a space group FM3-M.

The composition of the resulting compound was determined by ICP emissionspectral analysis and an inert gas fusion-infrared absorption method.

The results demonstrated that the compound had a composition ofLi₂MnO₂F.

Production of Positive Electrode Plate

Subsequently, 70 parts by mass of the resulting compound, 20 parts bymass of acetylene black, 10 parts by mass of poly(vinylidene fluoride),and an appropriate amount of N-methyl-2-pyrrolidone were mixed toprepare a positive electrode mixture slurry.

The positive electrode mixture slurry was applied to one surface of apositive electrode current collector formed of aluminum foil having athickness of 15 μm and was then dried in vacuum at 105° C. The positiveelectrode mixture slurry was thus dried and rolled and formed into a90-μm-thick positive electrode plate having a positive electrode activematerial layer.

Preparation of Nonaqueous Electrolytic Solution

LiPF₆ (CAS No. 21324-40-3) was dissolved at a concentration of 1.0 mol/Lin a solvent mixture (volume ratio: 20:80) of a cyclic solventfluoroethylene carbonate (hereinafter, referred to as FEC) (CAS No.114435-02-8) and a linear solvent methyl 3,3,3-trifluoropropionate(hereinafter, referred to as FMP) (CAS No. 18830-44-9) to prepare anonaqueous electrolytic solution.

Formation of Sheet Battery

FIG. 3 is a cross-sectional view illustrating a schematic structure ofthe battery in Example 1.

FIG. 4 is a perspective view illustrating a schematic structure of thebattery in Example 1.

In the sheet battery of Example 1, the electrode plate group isaccommodated in an outer packaging 4. The electrode plate group includesa positive electrode 21, a negative electrode 22, and a separator 14.The positive electrode 21 is composed of a positive electrode currentcollector 12 and a positive electrode active material layer 13 (positiveelectrode mixture layer). The positive electrode active material layer13 is disposed on the positive electrode current collector 12. Thepositive electrode 21 and the negative electrode 22 face each other withthe separator 14 interposed therebetween to form the electrode plategroup.

The positive electrode current collector 12 is connected to a positiveelectrode tab lead 1 c. The negative electrode 22 is connected to anegative electrode tab lead 2 c. The positive electrode tab lead 1 c andthe negative electrode tab lead 2 c extend to the outside of the outerpackaging 4.

A heat-bonded resin is arranged between the positive electrode tab lead1 c and the outer packaging 4. A heat-bonded resin is arranged betweenthe negative electrode tab lead 2 c and the outer packaging 4.

FIG. 5 is a diagram illustrating a schematic structure of the positiveelectrode plate in Example 1 and a method of producing the plate.

FIG. 6 is a diagram illustrating a schematic structure of the negativeelectrode plate in Example 1 and a method of producing the plate.

FIG. 7 is a perspective view illustrating a schematic structure of thebattery in Example 1.

The positive electrode plate was processed as shown in FIG. 5. Theelectrode mixture area was 4 cm² as shown in FIG. 5.

The negative electrode plate was processed as shown in FIG. 6. Thenegative electrode used was lithium metal foil having a thickness of 300μm.

As shown in FIG. 6, the positive electrode and the negative electrodewere placed so as to face each other with a separator (polypropylene,thickness: 30 μm) therebetween. Subsequently, 120×120 mm square aluminumlaminate (thickness: 100 μm) was folded, and the 120 mm edges wereheat-sealed at 230° C. into a tubular form of 120×60 mm. The electrodegroup comprising the facing electrodes as shown in FIG. 7 was insertedinto the tubular aluminum laminate from the 60 mm edge. As shown in FIG.3, the edge of the aluminum laminate was aligned with the heat-bondedresins of the tab leads and was heat-sealed at 230° C.; 0.35 cc of anonaqueous electrolytic solution was then poured in the tubular aluminumlaminate from the edge not sealed in dry air having a dew point of −60°C., followed by being left to stand under a vacuum of 0.06 MPa for 15minutes such that the electrolytic solution impregnated into theelectrode mixture; and finally, the edge of the laminate from which thesolution was poured was heat-sealed at 230° C.

As described above, a lithium secondary battery of Example 1 wasproduced.

Example 2

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent FEC and a linear solvent(2,2,2-trifluoroethyl)methyl carbonate (hereinafter, referred to asFEMC) (CAS No. 156783-95-8).

A lithium secondary battery was produced as in Example 1 except for theabove.

Example 3

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent FEC and a linear solvent2,2,2-trifluoroethylacetate (hereinafter, referred to as FEA) (CAS No.406-95-1).

A lithium secondary battery was produced as in Example 1 except for theabove.

Example 4

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:60:20) of a cyclic solvent FEC, a linear solvent FEMC, and alinear solvent FMP.

A lithium secondary battery was produced as in Example 1 except for theabove.

Example 5

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:60:20) of a cyclic solvent FEC, a linear solvent FEMC, and alinear solvent (2,2,2-trifluoroethyl)ethyl carbonate (hereinafter,referred to as FDEC) (CAS No. 156783-96-9).

A lithium secondary battery was produced as in Example 1 except for theabove.

Example 6

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:60:20) of a cyclic solvent FEC, a linear solvent FEMC, and alinear solvent methyl fluoroacetate (hereinafter, referred to as FMA)(CAS No. 453-18-9).

A lithium secondary battery was produced as in Example 1 except for theabove.

Example 7

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:10:70) of a cyclic solvent FEC, a cyclic solvent3,3,3-trifluoropropylene carbonate (hereinafter, referred to as FPC)(CAS No. 167951-80-6), and a linear solvent FEMC.

A lithium secondary battery was produced as in Example 1 except for theabove.

Example 8

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent FEC and a linear solvent ethyl methylcarbonate (hereinafter, referred to as EMC) (CAS No. 623-53-0).

A lithium secondary battery was produced as in Example 1 except for theabove.

Example 9

As the positive electrode active material,Li₂Ni_(0.33)Co_(0.33)Mn_(0.33)O₂F having a crystal structure belongingto a space group FM3-M was used instead of Li₂MnO₂F.

A lithium secondary battery was produced as in Example 1 except for theabove.

The positive electrode active material Li₂Ni_(0.33)Co_(0.33)Mn_(0.33)O₂Fwas synthesized by the same procedure as that of the synthesis ofLi₂MnO₂F except that LiNi_(0.33)Co_(0.33)Mn_(0.33)O₂ was used as a rawmaterial.

Example 10

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent FEC and a linear solvent EMC.

A lithium secondary battery was produced as in Example 9 except for theabove.

Example 11

As the positive electrode active material, Li₂CoO₂F having a crystalstructure belonging to a space group FM3-M was used instead of Li₂MnO₂F.

A lithium secondary battery was produced as in Example 1 except for theabove.

The positive electrode active material Li₂CoO₂F was synthesized by thesame procedure as that of the synthesis of Li₂MnO₂F except that LiCoO₂was used as a raw material.

Example 12

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent FEC and a linear solvent EMC.

A lithium secondary battery was produced as in Example 11 except for theabove.

Example 13

As the positive electrode active material, Li₂MnO_(1.5)F_(1.5) having acrystal structure belonging to a space group FM3-M was used instead ofLi₂MnO₂F.

A lithium secondary battery was produced as in Example 1 except for theabove.

The positive electrode active material Li₂MnO_(1.5)F_(1.5) wassynthesized by the same procedure as that of the synthesis of Li₂MnO₂Fexcept that Li₂O, LiF, MnO, and Mn₂O₃ were used as raw materials at amolar ratio Li₂O/LiF/MnO/Mn₂O₃ of 1/6/2/1.

Example 14

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent FEC and a linear solvent EMC.

A lithium secondary battery was produced as in Example 13 except for theabove.

Comparative Example 1

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent ethylene carbonate (hereinafter,referred to as EC) (CAS No. 96-49-1) and a linear solvent EMC.

A lithium secondary battery was produced as in Example 1 except for theabove.

Comparative Example 2

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent EC and a linear solvent EMC.

A lithium secondary battery was produced as in Example 9 except for theabove.

Comparative Example 3

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent EC and a linear solvent EMC.

A lithium secondary battery was produced as in Example 11 except for theabove.

Comparative Example 4

The nonaqueous electrolytic solution used was prepared by dissolvingLiPF₆ at a concentration of 1.0 mol/L in a solvent mixture (volumeratio: 20:80) of a cyclic solvent EC and a linear solvent EMC.

A lithium secondary battery was produced as in Example 13 except for theabove.

Comparative Example 5

As the positive electrode active material, LiCoO₂ having a crystalstructure belonging to a space group R3-M was used instead of Li₂MnO₂F.The positive electrode active material LiCoO₂ was synthesized inaccordance with a known procedure.

A lithium secondary battery was produced as in Example 1 except for theabove.

Evaluation of Battery

In the evaluation of the batteries produced as described above, eachbattery was sandwiched by stainless steel plates (thickness: 2 mm) of80×80 cm with the laminate, and the electrode plates were applied with apressure of 0.2 MPa by a U-shaped clamp. The evaluation was allperformed in a thermostat chamber of 25° C.

Charging and discharging at a constant current of 0.1 mA were repeatedtwo cycles such that the positive electrode is completely impregnatedwith the electrolytic solution. The charging and the discharging werestopped at battery voltages of 5.2 V and 1.5 V, respectively, and thebattery was left to stand during the interval between the charging andthe discharging for 20 minutes at an open circuit.

Subsequently, one cycle of charging and discharging was furtherperformed under the same conditions. The discharge efficiency (the valueobtained by dividing the discharge capacity by the charge capacity) ofthis third cycle was used as an index of reliability.

These results are shown in Table together with the results of dischargecapacity per weight of the positive electrode active material.

TABLE Positive electrode active Discharge capacity Discharge materialNonaqueous solvent (mAh/g) efficiency Example 1 Li₂MnO₂F FEC + FMP 34090% Example 2 Li₂MnO₂F FEC + FEMC 337 90% Example 3 Li₂MnO₂F FEC + FEA336 90% Example 4 Li₂MnO₂F FEC + FEMC + FMP 337 91% Example 5 Li₂MnO₂FFEC + FEMC + FDEC 335 91% Example 6 Li₂MnO₂F FEC + FEMC + FMA 332 89%Example 7 Li₂MnO₂F FEC + FPC + FEMC 332 89% Example 8 Li₂MnO₂F FEC + EMC332 81% Example 9 Li₂Ni_(0.33)Co_(0.33)Mn_(0.33)O₂F FEC + FMP 280 91%Example 10 Li₂Ni_(0.33)Co_(0.33)Mn_(0.33)O₂F FEC + EMC 275 80% Example11 Li₂CoO₂F FEC + FMP 232 89% Example 12 Li₂CoO₂F FEC + EMC 230 80%Example 13 Li₂MnO_(1.5)F_(1.5) FEC + FMP 265 89% Example 14Li₂MnO_(1.5)F_(1.5) FEC + EMC 265 89% Comparative Li₂MnO₂F EC + EMC 33578% Example 1 Comparative Li₂Ni_(0.33)Co_(0.33)Mn_(0.33)O₂F EC + EMC 27477% Example 2 Comparative Li₂CoO₂F EC + EMC 232 76% Example 3Comparative Li₂MnO_(1.5)F_(1.5) EC + EMC 261 78% Example 4 ComparativeLiCoO₂ FEC + FMP 180 85% Example 5

As shown in Table, the discharge efficiency of each battery of Examples1 to 8 is higher than that of the battery of Comparative Example 1.

This is probably caused by that in the positive electrode activematerial-nonaqueous solvent interfaces formed in the batteries ofExamples 1 to 8, side reactions hardly occur, compared to the battery ofComparative Example 1.

Similarly, the batteries of Examples 9 and 10, Examples 11 and 12, andExamples 13 and 14 have higher discharge efficiencies compared to thebatteries of Comparative Examples 2, 3, and 4, respectively.

Furthermore, the batteries of Examples 1 to 14 have higher dischargecapacities compared to that of Comparative Example 5.

The results described above demonstrate that the lithium secondarybattery according to the present disclosure has a high capacity and ahigh discharge efficiency (reliability).

The battery of the present disclosure can be suitably used as, forexample, a lithium secondary battery.

What is claimed is:
 1. A battery comprising: a positive electrodeincluding a positive electrode active material; a negative electrode;and an electrolytic solution including a nonaqueous solvent, wherein thepositive electrode active material includes a compound having a crystalstructure belonging to a space group FM-3M and represented byCompositional Formula (1):Li_(x)Me_(y)O_(α)F_(β)  (1) where Me is at least one element selectedfrom the group consisting of Mn, Co, Ni, Fe, Al, B, Ce, Si, Zr, Nb, Pr,Ti, W, Ge, Mo, Sn, Bi, Cu, Mg, Ca, Ba, Sr, Y, Zn, Ga, Er, La, Sm, Yb, V,and Cr; and subscripts x, y, α, and β satisfy the followingrequirements:1.7≤x<2,0.8≤y≤1.3,1≤α≤2.5,0.5≤β≤2, andx+y=α+β=3, and the nonaqueous solvent includes a solvent having at leastone fluoro group, wherein the solvent having at least one fluoro groupis included in the nonaqueous solvent at a volume percent ranging from20% to where the nonaqueous solvent is composed of substantially onlythe solvent having at least one fluoro group.
 2. The battery accordingto claim 1, wherein the solvent having at least one fluoro group is atleast one selected from the group consisting of a cyclic solvent and alinear solvent.
 3. The battery according to claim 1, wherein the solventhaving at least one fluoro group is at least one selected from the groupconsisting of carbonates, carboxylates, sulfones, and nitriles.
 4. Thebattery according to claim 3, wherein the solvent having at least onefluoro group is at least one selected from the group consisting ofcarbonates and carboxylates.
 5. The battery according to claim 4,wherein the solvent having at least one fluoro group is a compoundobtained by replacing one or more hydrogen atoms of a compound selectedfrom the group consisting of ethylene carbonate, propylene carbonate,butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, methyl acetate, methyl propionate, ethyl acetate, and ethylpropionate with an equal number of fluoro groups.
 6. The batteryaccording to claim 5, wherein the solvent having at least one fluorogroup is a compound obtained by replacing one or more hydrogen atoms ofa compound selected from the group consisting of ethylene carbonate,propylene carbonate, ethyl methyl carbonate, diethyl carbonate, methylacetate, methyl propionate, and ethyl acetate with an equal number offluoro groups.
 7. The battery according to claim 6, wherein the solventhaving at least one fluoro group is at least one compound selected fromthe group consisting of fluoroethylene carbonate,3,3,3-trifluoropropylene carbonate, (2,2,2-trifluoroethyl)methylcarbonate, (2,2,2-trifluoroethyl)ethyl carbonate, 2,2,2-trifluoroethylacetate, methyl 3,3,3-trifluoropropionate, and methyl fluoroacetate. 8.The battery according to claim 1, wherein the electrolytic solutionincludes a lithium salt; and the lithium salt is at least one selectedfrom the group consisting of LiBF₄, LiPF₆, LiN(SO₂CF₃)₂, LiN(SO₂F)₂, andlithium bis(oxalate)borate.
 9. The battery according to claim 1, whereinMe includes at least one selected from the group consisting of Mn, Co,and Ni.
 10. The battery according to claim 9, wherein Me is an elementselected from the group consisting of Mn and Co or is a solid solutioncomposed of Ni, Co, and Mn.
 11. The battery according to claim 1,wherein the positive electrode active material includes 90 wt % or moreof the compound.
 12. The battery according to claim 1, wherein thecompound satisfies1.79≤x<2;0.82≤y≤1.21;1.5≤α≤2.5; and0.5≤β≤1.5.
 13. The battery according to claim 12, wherein the compoundsatisfiesx<2;y=1;1.5≤α≤2; and1≤β≤1.5.